Disposable test sensor with improved sampling entrance

ABSTRACT

A disposable electrochemical test sensor designed to facilitate sampling of fluid samples. It has a fluid chamber having a novel extra wide sampling entrance, but no additional air escape vent. The chamber provides a reservoir from which a sample fluid can be drawn into the chamber through capillary action. The extra wide sampling entrance provided by the present invention can draw blood into the chamber through any part of the opening, thus it allows easy targeting the samples with small volume, picking up smeared samples and it is more tolerant to users who jam the tip of the sensor into users&#39; finger. The extra wide sampling entrance provided by the present invention also serves as air escape vent.

FIELD OF THE INVENTION

The present invention generally relates to a test sensor or strip. More specifically, the present invention generally relates to a disposable biosensor with a fluid chamber that is adapted to receive a fluid sample around with small volume. Still more specifically, the present invention generally relates an electrochemical biosensor with an extra wide sampling entrance. Still more specifically, the present invention relates methods of making and using the biosensors.

BACKGROUND OF THE INVENTION

The use of disposable test sensors such as strips in the medical field for testing various analytes in body fluid is well known. The accurate determination of analytes in body fluids is of great importance in the diagnoses of certain physiological abnormalities. In particular, it is important that diabetic individuals frequently check their glucose level in their body fluids to regulate the glucose intake in their daily diets. The results of such tests can be used to determine the insulin dosage or other medication needs to be administered. In one type of blood-glucose testing system, test sensors, or called glucose strips, are used by diabetic individuals to test a sample of blood in connection with a hand-held meter. The glucose strips are used by millions of diabetics throughout the world on a daily base.

There are hundreds of brand names of glucose strips in the market. They are very similar in terms of sensor construction: i.e., a channel is formed between a generally U-shaped spacer and is adapted to receive blood from the opening end of the sensor through capillary action and escape air from the other end through an air escape vent. In order to reduce blood volume, thus reduce pain from piercing finger or other sampling points, the blood receiving chamber is usually small and, as a result, the sampling entrance is also relatively small. As the volume of fluid chambers in the sensors decreases, it becomes increasingly more difficult to fill the fluid chamber with the sample to be analyzed. It has been observed that users may abuse the test sensor by jamming the tip of the test sensor into the individual's finger, which very probably results in incomplete blood filling, non-continuous filling or wiggling of blood flow. Additionally, in some existing test sensors, it is difficult to position the fluid sample within the channel entrance opening especially for those diabetics who have poor vision and/or trembling hand. Besides, blood samples turn to smear around the tip of fingers or other sampling points. It becomes very difficult to draw such smeared blood into the sensor chamber. All of these phenomena may eventually lead to biased readings, and as a result, wrong dosage of insulin administration and even life threatening errors may occur.

Therefore, in order to reduce or eliminate such biased readings caused by such user action and/or reduce the difficulty in connection with sampling, it would be highly desirable to have a more user friendly test sensor that could easily target sample, easily draw sample into the sensor chamber, and alleviate incomplete filling, non-continuous filling and other issues that may result in inaccurate test results. The present disclosure is directed to a novel design and method to overcome one or more of the limitations in the prior arts.

SUMMARY OF THE INVENTION

According to the first embodiment, a disposable electrochemical test sensor has a sample chamber having a novel extra wide sampling entrance, but no additional air escape vent. Such a design is adapted to improve sampling of fluid samples. The fluid chamber provides a reservoir from which sample fluid can be drawn into the sample receiving chamber through capillary action. The extra wide sampling entrance provided by the present invention can draw blood into the chamber through any part of the opening end. Thus it allows easily targeting the samples with small volume, picking up smeared samples and alleviating jamming the opening end. The extra wide sampling entrance provided by the present invention also serves as the air escape vent. Such one opening sensor eliminates over-flow issue often encountered in convenient sensors. In preferred embodiments, the sensor consists of multiple layers which include a base layer having conductive coatings serving as working and reference electrodes; a middle layer having semi-circular shape serving as spacer; and an upper layer with a hydrophilic surface facing to the chamber. The upper, middle and base layers are attached through adhesives or other ways to bond each other, such that the fluid chamber is formed between a portion of the lower layer surface and the upper layer surface at one end of the sensor, while the other end of the sensor having conductive layer exposed serve as electric contacts in connection with a monitor or meter.

According to the second embodiment, a disposable electrochemical test sensor has a sample chamber having a novel extra wide sampling entrance, but no additional air escape vent. Such a design is adapted to improve sampling of fluid samples. The chamber provides a reservoir from which sample fluid can be drawn into the sample receiving chamber through capillary action. The extra wide sampling entrance provided by the present invention can draw blood into the fluid chamber through any part of the front opening end, and can also draw blood into the fluid chamber through part of left side and part of right side near the opening end. The front opening and both side openings form a large opening, serving as blood sample entrance. Thus such unique design allows easily targeting the samples with small volume, picking up smeared samples and alleviating jamming of the opening by users' finger. The extra wide sampling entrance provided by the present invention also serves as the air escape vent. That is to say the air escape vent joins to the blood sampling entrance opening. Such two-in-one opening sensor eliminates over-flow issue often encountered in convenient sensors.

In preferred embodiments, the test sensor consists of multiple layers which include a base layer having conductive coatings serving as working and reference electrodes; a middle layer having semi-circular shape serving as spacer; and an upper layer with a hydrophilic surface facing to the chamber. The upper, middle and base layers are attached through adhesives or other ways to bond each other, such that the fluid chamber is formed between a portion of the lower layer surface and the upper layer surface at one end of the sensor, while the other end of the sensor having conductive layers exposed serve as electric contacts in connection with a monitor or meter.

According to one method, an analyte concentration is measured. A disposable electrochemical test sensor is provided having a sample chamber having a novel extra wide sampling entrance, but no additional air escape vent. The chamber provides a reservoir from which sample fluid can be drawn into the sample receiving chamber through capillary action. The extra wide sampling entrance provided by the present invention also serves as the air escape vent. In preferred embodiments, the sensor consists of multiple layers which include a base layer having conductive coatings serving as working and reference electrodes; a middle layer serves as spacer which may have different shapes, such as circular arc, square, rectangular, triangle, regular trapezoid, inverted trapezoid; and an upper layer with a hydrophilic surface facing to the chamber. The upper and base layers are attached through adhesives or other ways to bond each other, such that the fluid chamber is formed between a portion of the lower layer surface and the upper layer surface at one end of the sensor, while the other end of the sensor having conductive layers exposed serve as electric contacts in connection with a monitor or meter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a and 1 b are perspective views of the test sensor of the present invention according to the first (1 a) and second (1 b) embodiment.

FIG. 2 is an exploded view of the test sensor of the present invention showing the three component layers.

FIGS. 3 a and 3 b are top views of the test sensor of the present invention consisting of three laminated layers according to the first (3 a) and second (3 b) embodiment.

FIG. 4 is a top view of the base layer to be used in forming a test sensor according to one embodiment.

FIGS. 5 a and 5 b are top views of the middle layer to be used in forming a test sensor according to the first (5 a) and second (5 b) embodiment.

FIG. 6 is a top view of the upper layer to be used in forming a test sensor according to one embodiment.

FIG. 7 is a side view of the test sensor according to the first embodiment of the present invention.

FIG. 8 is a side view of the test sensor according to the second embodiment of the present invention.

FIGS. 9 a and 9 b illustrate blood entering the fluid chamber and air escape for the test sensor according to the first embodiment of the present invention. Solid arrows and blank arrows denote blood sampling directions and air escape directions, respectively.

FIGS. 10 a, 10 b and 10 c illustrate blood entering the fluid chamber and air escape for the test sensor according to the second embodiment of the present invention. Solid arrows and blank arrows denote blood sampling directions and air escape directions, respectively.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

The test sensor of the present invention is directed to improve sampling entrance of the strip for the determination of an analyte concentration of in a fluid sample, such as blood. In one embodiment, a test sensor is adapted to receive a fluid sample from one end of the sensor, while the other end is connected with an instrument or meter. Analytes that may be measured include, but not limited to glucose, lactate, uric acid, creatinine, creatine, cholesterol, triglycerides, hemoglobin, bilirubin, alcohol, etc. The fluid sample may be any body fluid, thus, the analytes may be in, for example, a whole blood sample, a blood serum sample, a blood plasma sample, other body fluids like tears, interstitial fluid and urine. In one preferred method, the testing equipment is a hand-held meter.

In one embodiment, the test sensor is an electrochemical test sensor. FIGS. 1 a and 1 b show perspective views of the test sensor of the present invention. The sensor has a sensor body 100, an electric contact end 10 and sampling end 20. The electric contact end may have at least two contacts used for one working electrode and one reference electrode, respectively. The sensor has a thin-layer fluid chamber 30 a and a thin-layer fluid chamber 30 b, according to the first embodiment and second embodiment, respectively. The thin-layer fluid chambers allow fluid sample to enter and also allow chemical reactions with the chemical reagents loaded on the surface of the electrodes, thus electrochemical signals, which correlate to the concentration of the analytes, can be generated.

FIG. 2 is an exploded view of the test sensor of the present invention showing the three component layers. In one preferred embodiment, the electric contact end has three electric contacts serving as contacts for a first working electrode 11; a second working electrode 13 and a reference electrode 12, respectively. In one embodiment, the test sensor consists of multiple layers which include a base layer 200; a middle layer 300; and an upper layer 400, as shown in FIG. 2.

FIGS. 3 a and 3 b are top views of the test sensor of the present invention consisting of three laminated layers according to the first (3 a) and second (3 b) embodiment. At the sampling end 20, there are three electrodes, corresponding to the first working electrode 31, second working electrode 33 and reference electrode 32. At electric contact end 10, there are three electric contacts 11, 12 and 13, connecting to the first working electrode 31; reference electrode 32; second working electrode 33; respectively. 91 denotes the side opening of the sampling entrance of the biosensor according to the second embodiment in the present invention.

FIG. 4 shows a top view of a first base layer 200 to be used in forming a test sensor according to one embodiment. The base layer 200 may be made from a variety of materials such as polymeric materials, coated with conductive materials such as carbon, various metals or metal oxides. The base layer 200 with conductive coating serves as substrate of the test sensor and chamber forming layer. It also serves as electrodes at one end 20 and electric contacts at the other end 10. Non-limiting examples of polymeric materials, that may be used to form the base layer include, but not limited to polyethylene, polypropylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene, polycarbonate, polyethylene terephthalate, polyethylene naphthalate, polyimide and combinations thereof. The conductive coating may be formed by a variety of methods which are well known in the field including, but not limited to printing (e.g., screen-printing), coating (e.g., reverse roll), vapor deposition, sputtering, chemical deposition, and electrochemical deposition. The conductive coating may be on a whole piece of insulating material. If so, a desired number of electric conduits must be made. This can be achieved by etching/scribing the required number of conductive conduits. The etching process may be accomplished chemically, by mechanically scribing lines in the conductive layer, or by using a laser to scribe the conductive layer into separate conductive conduits. The conductive materials may be, but not limited to various carbon materials; various noble metals like gold, platinum, palladium, iridium, rhodium, ruthenium; various metal oxides like indium oxide, tin oxide; and combinations thereof.

FIG. 5 a shows a top view of the middle layer 300 a to be used in forming a test sensor according to the first embodiment. The middle layer 300 a virtually has same width as the base layer 200, but shorter in length to leave part of the base layer 300 a for electric contacts. The middle layer 300 a serves as a spacer in between the base layer 200 and the upper layer 400. The middle layer 300 a, or spacer, is also made of a plastic insulating material with glue or adhesive on both sides and creates the thin-layer fluid chamber 30 a of the laminated body (FIGS. 1 a). It contains a semi-circular shaped cutout 41 a at the end 20 which overlays the base layer 200 with the open end corresponding to the open end of the laminated body described earlier. The semi-circular shaped cutout 41 a has a diameter of at least 1 mm. The diameter can be larger than or equal to the width of the base layer 200. More preferably, it is around 2 mm to 20 mm in the present invention. Assuming the test sensor or the component layers (200, 300 a and 400) in the present invention have a width of around 6 mm, preferably, the diameter of the semi-circular shaped cutout 41 a is around 5.2 mm. Thus, a blood sample can enter the thin-layer fluid chamber 30 a from any part of the entire opening end. A double coated, pressure-sensitive adhesive tape may be used as the middle layer 300 a. The cutout 41 a creating the thin-layer fluid chamber may have different shapes, including, but not limited to semi-circular, circular arc, square, rectangular, triangle, regular trapezoid, inverted trapezoid and etc. In one preferred embodiment, the cutout is in semi-circular shape. It can be seen in the figures that the thickness and size of the cutout 41 a determine the volume of the thin-layer fluid chamber 30 a. Preferably, the middle layer 300 a has a thickness ranging from 0.0 1mm to 0.5 mm, thus, the volume of the thin-layer fluid chamber 30 a is about 0.1 to 5 microliter in the present invention. More preferably, the middle layer 300 a has a thickness around 0.08 mm, thus, the volume of the thin-layer fluid chamber 30 a is about 0.85 microliter in the present invention.

FIG. 5 b shows a top view of the middle layer 300 b to be used in forming a test sensor according to the second embodiment. The middle layer 300 b is alternative to the middle layer 300 a according to the first embodiment. The middle layer 300 b also serves as a spacer in between the base layer 200 and the upper layer 400. The middle layer 300 b virtually has same width as the middle layer 300 a, but it is slightly shorter in length at the end 20, as a result, leaving openings at both corners after all three component layers 200, 300 b and 400 are laminated. Such a unique design of the present invention forms an over 180° sampling entrance, even wider opening compared to the first embodiment described above. Therefore, a blood sample not only enters the thin-layer fluid chamber 30 b from any part of the front opening, but also from both side opening 91 of the test sensor at the end 20, as shown in FIG. 3 b. The middle layer 300 b, or spacer, is also made of a plastic insulating material with glue or adhesive on both sides and creates the sample fluid chamber of the laminated body. It contains a semi-circular shaped cutout 41 b on the end 20 which overlays the base layer 200 with the open end corresponding to the open end of the laminated body described earlier. The semi-circular shaped cutout 41 b has a diameter of at least 1 mm. The diameter can be larger than or equal to the width of the base layer 200. Preferably, it is slightly smaller than the width of the base layer 200. More preferably, it is around 2 mm to 20 mm. Assuming the test sensor or the component layers (200, 300 b and 400) in the present invention has a width of around 6 mm, preferably, the diameter of the semi-circular shaped cutout 41 b is around 5.2 mm. A double coated, pressure-sensitive adhesive tape may be used as the middle layer 300 b. The cutout 41 b creating the fluid chamber may have different shapes, including, but not limited to semi-circular, circular arc, square, rectangular, triangle, regular trapezoid, inverted trapezoid and etc. In one preferred embodiment, the cutout is in semi-circular shape. The thickness and size of the cutout 41 b determine the volume of the thin-layer fluid chamber 30 b. Preferably, the middle layer 300 b has a thickness ranging from 0.01 mm to 0.5 mm, thus, the volume of the thin-layer fluid chamber 30 b is about 0.1 to 5 microliter in the present invention. More preferably, the middle layer 300 b has a thickness around 0.08 mm, thus, the volume of the thin-layer fluid chamber 30 b is about 0.85 microliter in the present invention.

The laminated body may also have an upper layer 400, as shown in FIG. 6, bonded to the middle layer 300 a or 300 b, but without an additional vent opening, which is needed in convenient sensors. It virtually has the same width as the base layer 200 and middle layers 300 a or 300 b, and it has the same length as the middle layer 300 a. The upper layer 400 is made of a plastic or polymer materials. Non-limiting examples of polymeric materials, that may be used to form the upper layer 400, include, but not limited to polyethylene, polyethylene terephthalate, polyethylene naphthalate, polyimide and combinations thereof. In one embodiment, the upper layer 400 has a hydrophilic surface facing to the chamber to facilitate the capillary action. It should be understood that the entire side of the upper layer 400 may be coated with a hydrophilic substance and then bonded to the middle layer 300 a or 300 b. In the present invention, it is not critical to have an additional vent opening at the upper layer 400.

Because of the unique design of the extra wide sampling entrance in the present invention, air escape is not an issue when a fluid sample such as blood enter the thin-layer fluid chamber. Air can always find a way to escape from some part of the wide opening. Convenient test sensors always contain a vent opening for air escape when a fluid sample enters capillary channels. However, such vent opening may often cause problems, such as overflow, that may generate erratic test results. Besides, users may accidently apply blood sample to the vent opening instead of the normal blood sampling entrance, that may also compromise the test results. The test sensor of the present invention with combination of sampling entrance and air escape vent in one extra wide opening virtually eliminates such issues.

FIG. 7 shows side view of the test sensor of the first embodiment consisting of three laminated layers including a base layer 200, middle layer 300 a and upper layer 400.

FIG. 8 shows side view of the test sensor of the second embodiment consisting of three laminated layers including a base layer 200, middle layer 300 b and upper layer 400. Note 91 denotes the side opening described earlier. It can be seen that its thickness is the same as or similar to the middle layer 300 b. The length of the side opening 91 is preferably from 0.01 mm to 2.5 mm. More preferably, it is from 0.1 to 0.3 mm. Still more preferably, it is around 0.25 mm. It should be emphasized that the side opening 91 in the unique design of the present invention is just a part of the extra wide sampling opening. The side and front opening combine to form an over 180° sampling angle.

The advantage of the test sensor in the present invention for blood sampling and air escape can be illustrated through FIGS. 9 and 10.

FIGS. 9 a, 9 b illustrate blood entering the fluid chamber and air escape for the test sensor according to the first embodiment of the present invention. Note solid arrows and blank arrows denote blood sampling directions and air escape directions, respectively. Because of the extra wide sampling entrance opening of the present invention, blood sample can enter the fluid chamber from any part of the front opening, while air escapes from the rest of the opening. For example, if blood sample enters from the middle of the opening, air can escape from both side of the front opening (FIG. 9 a); if blood sample enters from one side of the front opening, air can escape from the other side (FIG. 9 b).

FIGS. 10 a, 10 b, 10 c illustrate blood entering the fluid chamber and air escape for the test sensor according to the second embodiment of the present invention. Note solid arrows and blank arrows denote blood sampling directions and air escape directions, respectively. Because of the extra wide sampling entrance opening of the present invention, blood sample can enter the fluid chamber from any part of the over 180° opening, while air escapes from the rest of the opening. For example, if blood sample enters from the middle of the front opening, air can escape from both side of the front opening as well as from the side opening 91 (FIG. 10 a); if blood sample enters from one side of the front opening, air can escape from the other side of the front opening as well as from the side opening 91 (FIG. 10 b); if blood sample enters from one side opening 91, air can escape from the front opening as well as from the other side opening 91 (FIG. 10 c).

By having a test sensor with the extra wide openings in the first embodiment or second embodiment, being adapted to receive a fluid sample, the test sensor of the present invention more easily receives the fluid sample from a user and is more tolerant to users who jam the tip of the sensor into his/her finger, is more tolerant to fluid samples with very small volume (less than 1 microliter) and even smeared samples on the finger tip.

Referring back to FIGS. 1-3, the electrode 31, 32, 33 may be loaded with chemistries that react with an analyte to produce detectable electrochemical signals. The chemistries may contain an enzyme, an antibody, an antigen, a complexing reagent, a substrate or combination thereof. The reagents are selected to react with the desired analyte or analytes to be tested so as to assist in determining an analyte concentration of a fluid sample. In one embodiment, the reagents typically contain an enzyme such as, for example, glucose oxidase, glucose dehydrogenase, cholesterol oxidase, creatinine amidinohydrolase, lactate oxidase, peroxidase, uricase, xanthine oxidase and etc. which reacts with the analyte and with an electron acceptor such as a ferricyanide salt to produce an electrochemically measurable species that can be detected by the electrodes. For example, if the analyte of the test sensor is glucose, then glucose oxidase or glucose dehydrogenase may be included as the enzyme; if the analyte of the test sensor is uric acid, then uricase may be included as the enzyme. It should be noted that in some cases more than one enzyme may be included to construct the test sensor in order to generate detectable electrochemical signal. For example, in order to make a test sensor for cholesterol, cholesterol esterase, cholesterol oxidase and peroxidase may be included in the sensor.

In order for the test sensor works effectively, the electrode 31, 32, 33 may comprise a mixture of a polymer, an enzyme, a surfactant, an electron acceptor, an electron donor, a buffer, a stabilizer and a binder. The electrode 31, 32, 33 may further include a mediator that is an electron acceptor and assists in generating a current that corresponds to the analyte concentration. The preferable mediators could be redox chemicals either in oxidized or reduced form. The mediator used in the present invention may include, but not limited to various metal or noble metal complexes such as potassium ferricyanide, potassium ferrocyanide, cobalt phthalocyanine, various ferrocenes, and various organic redox mediators such as methylene blue, methylene green, 7,7,8,8-tetracyanoquinodimethane, tetrathiafulvalene, toluidine blue, meldola blue, N-methylphenazine methosulfate, phenyldiamines, 3,3′,5,5′-tetramethylbenzidine, pyrogallol, and benzoquinone, phenanthroline-5,6-dione and etc. For example, if the enzyme used to construct the test sensor is glucose oxidase or glucose dehydrogenase, then potassium ferricyanide may be included as redox mediator; if the enzyme used to construct the test sensor includes peroxidase, then potassium ferrocyanide may be included as redox mediator.

The electrode 31, 32, 33 include a first working electrode 31, a second working electrode 33 and a reference electrode 32. In one embodiment, the second working electrode 33 serves as a blank electrode without loading a chemistry that reacts with the analyte, such that background signal can be measured and be subtracted from the analyte signal resulted from the first working electrode 31. In this embodiment, effect of interference substances on the analyte signal could be minimized. The background signal may be generated from the matrix of the fluid sample. For example, if the test sensor is used to measure glucose in a blood sample, the background signals may be generated from ascorbic acid, acetaminophen, uric acid, bilirubin etc. in the blood sample. Still in, this embodiment, the electric signals such as current, impedance at the working electrodes 31 and 33, and time to obtain these signals could be used to estimate filling status of the thin-layer fluid chamber (filled or not). Thus, this embodiment could alert under-fill of fluid samples.

Although the description of test sensor construction above describes construction for a single sensor, the design and materials used can also be used for making multiple sensors from one large piece of each layer material. This would be accomplished by starting with relative large pieces of the base layer material, middle layer material and upper layer material. After a series of preparations described above, a plurality of multiple test sensors thus can be constructed to achieve mass production in a cost-effective way.

It should be noted that although the particular embodiments of the present invention have been described herein, the above description is merely for illustration purpose. Further modification and variations of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications and variations are deemed to be within the scope of the invention as defined by the appended claims. 

What is claimed is:
 1. An electrochemical test sensor comprising: a continuous base layer having a sampling end and an electric contact end and being coated with a conductive coating, the base layer having electrodes at the sampling end, and electric contacts at the electric contact end; a middle layer formed of an electrically insulating material having a width approximately equal to a width of the base layer, and having a sampling end and an electric contact end, the middle layer being attached to the base layer such that a portion of the electric contact end of the base layer extends beyond the electric contact end of the middle layer, the middle layer forming a cutout region defined by a portion of a front edge being recessed from the middle layer sampling end along nearly the entire width of the middle layer; a continuous upper layer having a sampling end and an electric contact end, the continuous upper layer being attached to the middle layer such that the electric contact end is aligned with the electric contact end of the middle layer; and a fluid chamber defined on a top by the continuous upper layer, on a bottom by the continuous base layer, on one side by the recessed edge of the middle layer defining the cutout region, and having a sampling entrance defined by an open side opposite to the one side, the fluid chamber sized and configured to receive a fluid by capillary action, and sized and configured to expose the electrodes of the base layer to the fluid.
 2. The electrochemical test sensor of claim 1 wherein the middle layer is formed of a two-sided adhesive tape.
 3. The electrochemical test sensor of claim 1 wherein the upper layer further comprises a hydrophilic material on a surface facing the fluid chamber.
 4. The electrochemical test sensor of claim 1 wherein the continuous upper layer prevents a passage of air through it, and wherein the continuous base layer prevents a passage of air through it.
 5. The electrochemical test sensor of claim 1 wherein the base layer further comprises a chemistry within the electrodes configured to cause an electrochemical signal once exposed to the fluid within the fluid chamber.
 6. The electrochemical test sensor of claim 1 wherein the sampling end of the middle layer is slightly recessed from a front edge of the upper layer sampling end and a front edge of the base layer sampling end.
 7. The electrochemical test sensor of claim 1 wherein the cutout of the middle layer is semi-circular, the semi-circular cutout having a diameter slightly less than the width of the middle layer.
 8. An electrochemical test sensor comprising: a base layer having a sampling end and an electric contact end and being coated with a conductive coating, the base layer having electrodes at the sampling end, and electric contacts at the electric contact end; a middle layer formed of an electrically insulating material having a width approximately equal to a width of the base layer, and having a sampling end and an electric contact end, the middle layer being attached to the base layer such that a portion of the electric contact end of the base layer extends beyond the electric contact end of the middle layer, the middle layer forming a semi-circular cutout region defined by a recessed front edge portion from the middle layer sampling end, a diameter of the semi-circular cutout region being slightly less than the width of the middle layer; an upper layer having a sampling end and an electric contact end, the upper layer being attached to the middle layer such that the sampling end is aligned with the sampling end of the middle layer and such that the electric contact end is aligned with the electric contact end of the middle layer; and a fluid chamber defined on a top by the upper layer, on a bottom by the base layer, on one side by the recessed edge of the middle layer defining the cutout region, and having a sampling entrance defined by an open side opposite to the one side, the fluid chamber sized and configured to receive a fluid by capillary action, and sized and configured to expose the electrodes of the base layer to the fluid.
 9. The electrochemical test sensor of claim 8 wherein the middle layer is formed of a two-sided adhesive tape.
 10. The electrochemical test sensor of claim 8 wherein the upper layer further comprises a hydrophilic material on a surface facing the fluid chamber.
 11. The electrochemical test sensor of claim 8 wherein the upper layer is a continuous layer that prevents a passage of air through it, and wherein the base layer is a continuous layer that prevents a passage of air through it.
 12. The electrochemical test sensor of claim 8 wherein the base layer further comprises a chemical composition within the electrodes configured to cause an electrochemical signal once exposed to the fluid within the fluid chamber.
 13. The electrochemical test sensor of claim 8 wherein the sampling end of the middle layer is slightly recessed from the front edges of the upper layer sampling end and the base layer sampling end.
 14. An electrochemical test sensor comprising: a base layer having a sampling end and an electric contact end and being coated with a conductive coating, the base layer having electrodes at the sampling end, and electric contacts at the electric contact end; a middle layer formed of an electrically insulating material having a width approximately equal to a width of the base layer, and having a sampling end and an electric contact end, the middle layer being attached to the base layer such that a portion of the electric contact end of the base layer extends beyond the electric contact end of the middle layer, while a portion of the base sampling end extends beyond the middle layer sampling end, the middle layer forming a semi-circular cutout region defined by a recessed front edge portion from the middle layer sampling end, a diameter of the semi-circular cutout region being slightly less than the width of the middle layer; an upper layer having a sampling end and an electric contact end, the upper layer being attached to the middle layer such that the upper layer sampling end extends slightly beyond the middle layer sampling end, and such that the electric contact end is aligned with the electric contact end of the middle layer; a fluid chamber defined on a top by the upper layer, on a bottom by the base layer, on one side by the recessed edge of the middle layer defining the cutout region, and having a sampling entrance on an open side opposite to the one side; wherein the upper layer, middle layer, and base layer define two side openings in communication with the fluid chamber, the two side openings being defined by the upper layer and base layer extending beyond the sampling end of the middle layer; and wherein the fluid chamber is sized and configured to receive a fluid by capillary action, and sized and configured to expose the electrodes of the base layer to the fluid.
 15. The electrochemical test sensor of claim 14 wherein the middle layer is formed of a two-sided adhesive tape.
 16. The electrochemical test sensor of claim 14 wherein the upper layer further comprises a hydrophilic material on a surface facing the fluid chamber.
 17. The electrochemical test sensor of claim 14 wherein the upper layer is a continuous layer that prevents a passage of air through it, and wherein the base layer is a continuous layer that prevents a passage of air through it.
 18. The electrochemical test sensor of claim 14 wherein the base layer further comprises a chemistry within the electrodes configured to cause an electrochemical signal once exposed to the fluid within the fluid chamber.
 19. The electrochemical test sensor of claim 14 wherein the sampling entrance comprises the open side, and the two side openings, the open side being along an entire front width of the sensor, the two side openings being adjacent to the open side, and defining a continuous opening.
 20. The electrochemical test sensor of claim 19 wherein the sampling entrance is sized to allow an escape of air simultaneously with an entrance of fluid. 